DESCRIPTION: The study seeks to determine if exercise training above the measured lactic threshold improves performance more than training below the lactic threshold in patients with chronic obstructive pulmonary disease (COPD); to determine if delayed release of lactic acids of blood results in a reduction of dyspnea; and to determine if changes in lactic acid in dyspnea translate into improved quality of life. The working hypotheses are that exercise training will reduce dyspnea by circulating lactic acid; high intensity training will improve function more and reduce lactic acid to a greater extent than low intensity training; and the benefits of exercise training will improve measured quality of life. Recent data indicate that education in other cognitive interventions failed to alter functional capacity in dyspnea patients with COPD. Rehabilitation, specifically exercise intervention, has resulted in performance gains for patients. The results of rehabilitation training, however, are variable, suggesting that exercise training has not yet been optimized. Patients will be randomly assigned to one of two experimental groups; high intensity versus low intensity exercise training. Randomization will also be blocked by smoking status. Prior to the intervention, measurement of respiratory gas exchange, acid, dyspnea, and quality of life will be used to stratify the patients. Patients will complete 16 weeks of supervised exercise training followed by a long-term maintenance program for total follow-up of one year. The primary endpoints are changes in the lactic threshold and dyspnea, with the assumption that these should translate into improved quality of life.